1. Field of the Invention
The present invention generally relates to a directional antenna and, more particularly, to a relatively broad band high gain short backfire antenna.
2. Description of the Prior Art
In U.S. Pat. Nos. 3,438,043 and 3,508,278 short backfire antennas are described. Basically, the antenna taught therein consists of a main planar reflector, a feed element, such as a dipole, in front of the planar reflector, and a second reflector in the form of a plurality of dipoles or a flat disc, serving as a splash plate in front of the feed element. Such an antenna, i.e., one with a planar main reflector has several very significant limitations. If a large aperture, say on the order of more than 3.lambda. is required to produce a narrow beam with high gain the energy does not collimate well by the planar reflector with the single feed element. Thus, an array of feed elements is required. Also, the bandwidth of the antenna with the planar reflector is relatively limited. Furthermore, spillover in the prior art antenna, even when employing a rim around the planar reflector, is quite high which is undesirable, since it increases the noise and may affect adjacent antennas. Also, in the prior art antenna the back radiation of the feed element is quite high and the radiation pattern in the E and H planes is not equalized, resulting in higher cross polarization, all of which reduce the antenna efficiency.